It has become known from U.S. Pat. No. 4,243,306 to use for such pads materials within the hardness range of 10-30 Shore-D, measured according to DIN 53 505. It is furthermore known therefrom that silicone rubber is suitable for this purpose. DIN 53505 is entitled "Testing of Elastomers; Shore A and D Hardness Testing." It describes a method of determining the hardness of elastomers. In relevant part, DIN 53505 states:
The Shore hardness means the resistance to penetration by a body of defined shape under a defined compressive load. The hardness scale covers the range from 0 to 100, 0 representing the least and 100 the greatest hardness.
The method and apparatus for performing Shore hardness testing and measurement also are described in American Society of Testing Materials (ASTM) Standard D 2240-85, entitled "Standard Test Method for Rubber Property--Durometer Hardness.
In principle, there are in existence different kinds of pads, viz.:
(a) Pads which are fastened to a pad ever by means of retention pins, these pads being supported not only by the retention pins, but also by the pad lever which, for its part, carries the retention pins and which extends along a step in the pad as shown, for example, in FIGS. 3 and 4 of U.S. Pat. No. 4,243,306.
(b) Another kind of pad comprises, cast-in, a sleeve in a somewhat harder material and provided with a blind hole, into which the pad lever is inserted. U.S. Pat. No. 4,235,530 shows such a solution.
(c) Another kind of pad is kidney-shaped, consisting of an elastic pad base material and comprises, cast-in, a flat anchoring plate in a hard material, for example metal. This plate is connected to a finger which projects from the surface which is directed away from the skin contact surface of the pad. The finger has a cross bore and forms part of a semicardanic or fully cardanic suspension on the pad lever. Such a solution is known from DE OS 27 50 910.
(d) Finally, there are in existence further pads which are connected directly to the spectacle frame, as known from U.S. Pat. No. 4,142,784.